Just another weblog

There may by cases where you want to gen­er­ate a Linux binary on a FreeBSD machine. This is not a prob­lem with the lin­ux­u­la­tor, but not with the default linux_base port.

As you may know, the linux_base port is designed to deliver an inte­grated expe­ri­ence with FreeBSD native pro­grams. As such some parts of the native FreeBSD infra­struc­ture is used. If you would try to use a Linux–com­piler to gen­er­ate Linux–bina­ries, you would run into the prob­lem that by default the FreeBSD includes are used.

Pre­req­ui­sites

To have a fully fea­tured and non-integrated Linux envi­ron­ment on your FreeBSD sys­tem either mount an exist­ing (and com­pat­i­ble) Linux instal­la­tion some­where into your FreeBSD sys­tem, or install a linux_dist port. This can be done addi­tion­ally to an already installed linux_base port.

Prepa­ra­tion

When you have a com­plete Linux envi­ron­ment avail­able, you need to mount the FreeBSD devfs to /path/to/complete_linux/dev, lin­procfs to /path/to/complete_linux/proc and lin­sysfs to /path/to/complete_linux/sys to have a com­plete setup.

Use it

Now you just need to chroot into this /path/to/complete_linux and you configure/make/install or what­ever you need to do to gen­er­ate your desired Linux binary.

A while ago I com­mit­ted the lin­ux­u­la­tor D-Trace probes I talked about ear­lier. I waited a lit­tle bit for this announce­ment to make sure I have not bro­ken any­thing. Nobody com­plained so far, so I assume noth­ing obvi­ously bad crept in.

The >500 probes I com­mit­ted do not cover the entire lin­ux­u­la­tor, but are a good start. Adding new ones is straight for­ward, if some­one is inter­ested in a junior–ker­nel–hacker task, this would be one. Just ask me (or ask on emu­la­tion@), and I can guide you through it.

I updated my lin­ux­u­la­tor-dtrace patch to a recent –cur­rent. I already com­piled it on i386 and arundel@ has it com­piled on amd64. I counted more than 500 new DTrace probes. Now that DTrace res­cans for SDT probes when a ker­nel mod­ule is loaded, there is no ker­nel panic any­more when the linux mod­ule is loaded after the DTrace mod­ules and you want to use DTrace. I try to com­mit this at a morn­ing of a day where I can fix things dur­ing the day in case some prob­lems show up which I did not notice dur­ing my testing.

I set the expi­ra­tion date of linux_base-fc4 (only used by 7.x and upstream way past its EoL) and all depen­dent ports. It is set to the EoL of the last 7.x release, which can not use a later linux_base port. I also added a com­ment which explains that the date is the EoL of the last 7.x release.

Last week­end I com­mit­ted some dummy-syscalls to the lin­ux­u­la­tor in FreeBSD–cur­rent. I also added some com­ments to syscalls.master which should give a hint which linuxker­nel had them for the first time (if the linux man-page I looked this up in is cor­rect). So if some­one wants to exper­i­ment with a higher com­pat.linux.osrelease than 2.6.16 (as it is needed for a Cen­tOS based linux_base), he should now get some ker­nel mes­sages about unim­ple­mented syscalls instead of a silent failure.

There may be some low-hanging fruits in there, but I did not really ver­ify this by check­ing what the dummy syscalls are sup­posed to do in linux and if we can eas­ily map this to exist­ing FreeBSD fea­tures. In case some­one has a look, please send an email to emulation@FreeBSD.org.